Please reply to me here on this original question thread. Do not open a brand new question to respond to me. It is more efficient and less confusing for all the dialogue we share about this incident to appear on the same question thread.
It sounds as if there are issues related to your detention, the questioning and search and seizure. Without a great deal more information, I cannot tell if the police acted legally or not. I can invent a scenario where everything they did was proper, but I can certainly come up with scenarios where your Constitutional rights were infringed upon.
At this point, I see as questionable the length of the detention, the questioning you -- unless they gave you Miranda warnings -- the seizure of your backpack and the delay in the arrest. All I can say is, that now that you have been charged with a crime, you will start seeing the police reports and you and your lawyer will be able to get a sense of whether the seizure that led to your arrest was improper.
The way such Constitutional issues are explored and expressed has been set down by the US Supreme Court. Matters involving 4th and 5th Amendment violations are not written in stone. They must be investigated on a case by case basis at pre-trial suppression hearings. Your lawyer will be able to move for such a hearing. The standard that the judge uses for the hearing has also been set by the US Supreme Court. And that is whether the police acted reasonably under all the facts and circumstances.
So, at these hearings, the prosecutor will put the officer on the stand and have him explain why you were stopped, detained, questioned, searched and why your backpack was seized. He will also have to explain how the arrest came about. All of the prosecutor's questions will be designed to make the police officer appear as reasonable as possible under the circumstances.
When he is finished, your lawyer would get to question the police officer, and he would do his best to show how UNreasonable the police action was -- how you were detained for too long without probable cause, how you were questioned without being Mirandized (if that was the case), and how your property was wrongfully seized without basis.
When both sides have rested, the judge will make a decision as to whether the police violated your rights. If it is determined that they overstepped their bounds with regard to you, evidence taken from you could not be used against you at your trial. If this is a drug case and it was drugs found in your bag and there were no other charges against you, this would result in the dismissal of your case.